1. Field of the Invention
The present invention generally relates to an optical device, in particular, to a testing device having a dark field photograph for detecting a surface defect of an object.
2. Description of Prior Art
At present, dark field lighting technology is comprehensively applied to the testing procedure of an element or an object having a structure of mirror surfaces, for example, to the defect detection of surfaces of jewel, gem, and semiconductor element, etc. Essentially, a dark field lighting technology is to apply a light source to generate a light incident directly upon an object to be tested, through the diffusively reflective or refractive characteristics thereof, the diffusively reflected or refracted light forming an image, from which a defect on the tested object may be detected.
As shown in FIG. 1, which is a dark field testing device commonly seen, and the device includes: a cavity 10, the interior surfaces of which are all made of light-absorbing materials; an opening 101 arranged on the top of the cavity 10; a plate body 20 arranged in corresponding to the opening 101; a lighting element 30 arranged at the bottom of the cavity 10; a plurality of light-guiding tubes 40 closely surrounding the lighting elements 30 to guide the light from a light source toward an object 50 to be tested; and, a platform 102, on which the tested object is placed, and by which the light emitted from the lighting element 30 is blocked, such that the light guided by the light-guiding tubes 40 are directly incident upon the object 50 to be tested, which has the characteristics of reflection or refraction to focus an image on the surface of the plate body 20, whereby the optical image may be judged to determine whether a defect exists on the surface of the tested object or not.
However, in the prior detecting device, in which light-guiding tubes 40 are served as light-guiding paths and light sources of the dark field lighting, the object 50 to be tested has to be placed directly on the platform 102 with an artificially turning or rotating way to make the light of the light-guiding tube 40 incident upon the object to be tested from every aspect. Not only the testing efficiency is deteriorated, but also it easily results too insufficient light source to focus into an image through reflection and refraction, by applying the light-guiding tubes 40 as light-guiding paths, thanks to an indirectly lighting manner, so during testing judgment, this kind of uncertainty will influence the testing accuracy and becomes a problem needed to be solved urgently by those who are skilled in this art.